A widely used apparatus for optometric measurements is known as a phoropter. It usually comprises a trial frame which carries interchangeable lenses and an eye chart. The subject whose sight is being tested views the eye chart through the trial frame and the optometrist select lenses from a graduated set, interchanging them until the subject has the subjective feeling of optimum visual acuity. This trial and error process is known as a subjective refraction test or vision test. The vision test may be more automated by means of an electro-mechanical lens changer; however, in all the test procedures, the test is performed stepwise, making it difficult for subjects to determine the optimum correction lens combination.
Several recent publications have proposed new ways of doing optometric measurements. Instead of using a trial frame with interchangeable lenses, it is disclosed to use optical elements with variable and controllable spatial phase properties (“adaptative optical elements”), e.g. continuously variable optical lenses, to obtain optimum subjective correction (see for example published patent applications WO2006092804, US2004100617 or EP1569546).
FIG. 1 illustrates an apparatus described for example in published patent application WO2006092804 in the name of Abitbol. The subject 10 views an eye chart 12, for example a test card, located at a given distance from him, through a trial frame 14 incorporating a pair of electronically continuously variable optical lenses, for example electrowetting lens elements 16. In the following, such trial frame may be either named a “trial frame with variable lenses”, or “variable lens frame”, or “frame with variable lenses”. Such electrowetting lenses are described for example in U.S. Pat. No. 6,369,954 in the name of Berge et al. In standard vision tests, while an eye is obstructed by a shutter, the other eye views the eye chart through the variable lens. The subject may adjust the form of the electrowetting lens 16 until the best visual acuity is obtained for the tested eye, as determined by the subjective perception of the subject. A unit control 26 outputs drive voltages 25 to the electrodes of each of the electrowetting lenses 16 according to the settings of control inputs 28. These drive voltages may be adjusted by the subject himself, to provide the best visual acuity of the test card. As disclosed in WO2006092804, the described method may apply to other parameters than the focus, e.g. Astigmatism, astigmatism orientation, or even higher order aberrations. This is made possible by using a multi electrodes electrowetting lens as described for example in U.S. Pat. No. 6,538,823, a patent in the name of Kroupenkine et al.
In all cases, the optimization of the correction is made according to the perceived visual acuity of the test card by the subject, which may result from the sharpness and contrast of the test chart. However, discriminating according to chart contrasts may add stress to some subjects. Also when the doctor is controlling the control inputs, the translation of the subject's impression to the doctor can be biased by the stress of the relationship doctor-subject. Further, some subjects find it uncomfortable to have one eye tested, while the other eye is in the dark. In general the stress generated to the subject leads to a wrong correction: indeed vision is affected by any emotional state. In order to achieve a good vision test, the subject should be relaxed, as he or she is in usual daily life.
The present invention provides new methods and devices for optometric measurements that provide a subjective vision test with limited stress for the subject and a better accuracy of the correction.
More generally, the present invention provides new methods and devices for interactive adjustment of a parameter of a continuously variable optical lens.
The disclosures of the publications mentioned in this section and in other sections of the specification are incorporated herein by reference, each in its entirety.